1. Field of the Invention
The present invention relates to a power control apparatus and an unlocking apparatus suitably used for an audio/video (AV) system or the like.
2. Description of the Prior Art
It is known that a plurality of AV apparatuses such as a video tape recorder (VTR) and a laser disc player (LDP) are connected to an AV center (that is, a television) for example and each of the AV apparatuses turns off its power when it is out of use for a certain period of time.
It is also known that, in an D2B (abbreviation for Domestic Digital Bus) bus system, during communication from a master apparatus to a slave apparatus, the master apparatus issues a locking instruction to the slave apparatus to lock it against an interrupt from another master apparatus; the slave apparatus thus locked rejects any interrupt from another master apparatus until unlocked by the locking master apparatus. However, if no unlocking instruction is issued from the master apparatus to the slave apparatus due to an operation error or a timing error for example, the slave apparatus is left locked, is unable to accept an instruction from another master apparatus. To avoid such a problem, a conventional method is used in which a slave apparatus, upon reception of a locking instruction from a master apparatus, sets its lock timer and monitors a timer value in a main routine. If no data comes after a certain period of time, the slave apparatus resets a locking flag to get out of a locked state.
However, if each of the apparatuses connected to the AV center turns off its power, it poses the risk of turning off a power to an AV apparatus which is necessary for the AV center.
It is known that processing of the conventional D2B bus system is divided into receive interrupt processing and main processing. In the main processing, bus data received by the receive interrupt processing is sorted to be processed. For example, if a connection command is to be sent from this apparatus to a lower-layer apparatus as instructed by a command received by the receive interrupt processing in the main processing, processing for transmission to the D2B bus must be performed at the same time. Further, a packet-to-packet send wait time at sending must be controlled and inner bus communication processing must be performed at the same time. These processing operations are looped in the main routine and are controlled by corresponding processing flags and timer flags. Consequently, in the conventional method, performing the above-mentioned processing operations including the locking timer monitoring in the main routine requires checking each other's progress, making a program totally complicated and consuming a lot of time for program debugging and maintenance.